Starting of SAP system is performed in multiple steps and it is done my SAP Administrator user <sid>adm.
Step 1. Start database
The core of entire SAP system is its database. So database is started first.
Step 2. Start Central Service Instance (CSI)
Start the Central Service Instance that contains both enqueue and message service for the Java part of SAP. The central Services are installed as an independent instance.
Step 3. Start central Instance.
After the start of database and CSI next we see that is operating system collector SAPOSCOL is active or not. If not already active then we start it.
The Central Instance with its message server, dispatcher and workprocesses is started.
Step 4. Start Dialog Instance
If we don’t have dialog instance running on the same host as the central instance, then SAPOSCOL is started (if not running), then dispatcher along with its workprocess is started.